As a means for converting renewable-energy existing in nature to power energy, a wind power generation system and a solar photovoltaic system are used. The energy sources of the wind power generation system and solar photovoltaic system are wind energy and solar energy that change with time, so that the generation power of the power generation system changes with time.
The power system adjusts the generation power of a thermal power station, a hydroelectric power station, or a pumping-up electric power station according to the magnitude of power demands, thereby keeping balance with power demands. Therefore, when a greatly-changeable power source of the wind power generation system or solar photovoltaic system is connected to the power system in a large quantity, there is a worry about insufficient adjustment of the balance in supply and demand and enlargement of the frequency change.
To avoid it, it is necessary to install a power storage apparatus in the wind power generation system or the solar photovoltaic system and provide a means for charging and discharging changeable generation power of the wind power generation system or the solar photovoltaic system by the power storage apparatus, thereby relieving the power change outputted to the power system.
As a power storage apparatus for relieving the power change of natural energy, in Japanese Patent Laid-open No. 2007-306670, a charging and discharging art for preventing the storage electric energy of a storage battery from being deviated to the upper limit value or the lower limit value for a long period of time is described.
As the power generation capacity of the power generation system such as the wind power generation system or the solar photovoltaic system is enlarged, the power compensation capacity of the power storage apparatus is also increased greatly. A large capacity of the power storage apparatus can be generally realized by connecting a plurality of electricity storage devices including secondary batteries and power control units in parallel. Therefore, it is necessary to decide a distribution method of a charge and discharge power instruction to the plurality of electricity storage devices.
As a power instruction distribution method of the power storage apparatus composed of a plurality of electricity storage devices, for example, in Japanese Patent Laid-open No. 2009-044862, an art for a power source control unit of an electric car to detect the deterioration condition of the secondary batteries and distribute a small quantity of the power instruction to the deterioration-progressed electricity storage device is described.
Further, in the wind power generation system including the power storage apparatus, as an art for relieving the power change and reducing the power loss accompanying the charge and discharge of the storage batteries, a power generation system structured so as to decide, from the maximum value and minimum value of the output power of the wind power generation apparatus and power storage apparatus in the past for a given period, the outputtable range in the next period and decide the charge and discharge electric energy of the power storage apparatus and a power limit instruction of the wind power generation apparatus so as to control the output power of the wind power generation apparatus and power storage apparatus within the outputtable range is disclosed in Japanese Patent Laid-open No. 2009-079559.